1. Field of the Invention
The present invention relates to a heat-curable resin composition and its use. The heat-curable resin composition is suitably applied to coating compositions, adhesives, shaped articles, sealing resins for photosemiconductors, or coating liquids for forming protective films of color filters of liquid crystal displays (LCD), solid-state image sensors such as charge coupled device (CCD), or electroluminescent (EL) devices, etc.
2. Description of the Prior Art
Automobile coatings, architectural coatings, and adhesives and shaped articles used in these industrial applications are required to be highly durable and have been produced from heat-curable resins capable of forming a rigid three-dimensional crosslinking structure by heating.
In recent years, color liquid crystal displays (LCD) are rapidly spread as flat panel displays for personal computers, etc. For such color LCD, color filters are essential parts for realizing full color display. In general, the color filter is provided with a protective film to cover and protect the color layers of red (R), green (G) and blue (B). The protective film is required to have sufficient hardness and adhesion property as well as excellent transparency and uniform thickness so as not to adversely affect the pixel colors. To prevent the contamination of the contacting liquid crystal, the protective film is further required to have anti-contamination properties such as passivation properties for preventing contaminants from transferring from the colored layer to liquid crystal and have insolubility to liquid crystal for preventing the protective film itself from dissolving into liquid crystal. In addition, the protective film is required to be high or good in various properties such as heat resistance, hardness, resistance to warm pure water, solvent resistance and storage stability. Also, as photosemiconductors for LCD, a high luminance blue LED and white LED have been developed and their applications have been broadened to backlights for display boards, full color displays and cellular phones, etc.
In the production of these coating compositions, adhesives, shape articles, protective films for color filters and sealing materials for photoelectric transducers such as LED, epoxy/acid anhydride curing type heat-curable resins have been used because of their excellent colorless transparency. As the curing agents for such heat-curable resins, there have been used alicyclic acid anhydrides such as methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride and tetrahydrophthalic anhydride.
However, since the above compounds show only a low curing reactivity, a curing accelerator must be additionally used to fully cure the heat-curable resins.
As such curing accelerators, for example, triphenylphosphonium bromide (JP 2000-344868A), 2-ethyl-4-methylimidazole (JP 2001-114868A), ethylhexane salt of 1,8-diazabicyclo[5.4.0]undecene-7 (JP 2002-97251A), and tetraphenylphosphonium bromide (JP 2003-26763A) have been used.
To apply the heat-curable resin compositions to coating liquids for forming protective films of color filters or semiconductors such as blue LED and white LED, the heat-curable resin compositions must retain a good colorless transparency for a long period of time. In LCD application fields, COG (chip on glass) liquid crystal devices, etc. come to be widely used in overhead projector applications. In photosemiconductor applications, there has been made a rapid advancement in increasing the luminance of LED. Therefore, the protective films of color filters and the sealing resins come to be exposed to higher temperatures and lights of higher energy to cause discoloration (yellowing), making it difficult to maintain the colorless transparency for a long period of time. One of the causes of the discoloration (yellowing) is the change in phenyl group of the acid anhydride-based curing agent (e.g., trimellitic anhydride) contained in the heat-curable resin compositions (for example, as described in JP 2001-158816A). Therefore, the use of curing agents containing an aromatic group in their molecular structure is undesirable. In addition, the phenyl group or nitrogen component in the curing accelerators may cause the discoloration (yellowing) of the heat-curable resin compositions. Therefore, the use of the curing accelerator in coating liquids for forming protective films of color filters or sealing resins for semiconductors is also undesirable in view of maintaining a good colorless transparency of the heat-curable resin compositions.